1. Technical Field
The invention relates to a driving circuit of a flat display. Particularly, the invention relates to a driving circuit having a thermal-reducing effect.
2. Related Art
A display panel of a flat display is composed of a pixel array. Each pixel may contain a plurality of sub-pixel colors corresponding to primary colors, and display a brightness of a color according to a required gray level, so as to form the color of a color pixel. A driving voltage of each pixel varies with the gray level. Regarding dynamic images, the display panel continuously displays new frames according to a frequency, and accordingly charges/discharges the driven pixels.
FIG. 1 is a schematic diagram of a conventional driving circuit of a flat display. The conventional driving circuit 102 of the flat display receives a voltage input signal Vin of a voltage input circuit 100 to charge or discharge a pixel capacitor 116 of a corresponding pixel of a display panel 104 of the flat display, so as to achieve a voltage corresponding to the voltage input signal Vin to display a desired gray level. In a general structure, the voltage input circuit 100, such as an operation amplifier, amplifies to a voltage used for controlling the driving circuit according to a digital gray level, which is referred to as Vin. The driving circuit 102 charges the pixel capacitor 116 of the pixel, and the pixel circuit has a pixel resistance 114 represented by an impedance value of RP.
The driving circuit 102 generally includes a charging circuit path and a discharging circuit path. The charging circuit path, for example, includes a P-type metal oxide semiconductor (PMOS) transistor 106, a switch 110 and an electrostatic discharge (ESD) element 112, and impedances thereof are respectively represented by RSP, RS and RE. The discharging circuit path, for example, includes an NMOS transistor 108, the switch 110 and the ESD element 112. An impedance of the NMOS transistor 108 is represented by RSN. Gates of the PMOS transistor 106 and the NMOS transistor 108 are controlled by the voltage input circuit 100 under normal operation, and conducting levels of the transistors are controlled by the gray levels.
In a charging stage, a system high voltage VDD is received, and the pixel capacitor 116 is charged according to the input voltage Vin. A capacitance of the pixel capacitor 116 is represented by CP, which becomes stable after a period of time, and an output voltage Vout at an output terminal of the driving circuit 102 increases with time in the charging stage. In a discharging stage, a ground voltage provides a discharging voltage.
Since the internal impedance of the driving circuit may have power consumption during a driving process, heat is generated. When a pixel density increases, the generated heat cannot be ignored. Therefore, it is an important issue in research and development to reduce a temperature of the driving circuit.